I was trying to reset the data, and want to go to initial state ,I know that the immutability playing major role in this part.
Below is my store data (Flow Completed data)
animalSense: {
selectedVision: 'dayLight',
selectedState: 'california',
viewedVisions: ['dayLightcalifornia', 'dayLightsouthAfrica', 'nightVisioncalifornia'],
viewedAnimals: ['dog', 'cat']
},
I want to replace it with the below data
animalSense: {
selectedVision: '',
selectedState: '',
viewedVisions: [''],
viewedAnimals: []
},
I know the below action is the Straight and proper way to add initial data is
export const RESET_ANIMAL_SENSES = 'actions/reset_animal_senses';
export default () => ({
type: RESET_ANIMAL_SENSES,
payload: {
selectedVision: '',
selectedState: '',
selectedAnimal: '',
viewedVisions: [''],
viewedAnimals: []
}
});
But the above action maintaining the same state
Below action is Working Solution but I don't know is this a Proper way
export const RESET_ANIMAL_SENSES = 'actions/reset_animal_senses';
const data = JSON.stringify({
selectedVision: '',
selectedState: '',
selectedAnimal: '',
viewedVisions: [''],
viewedAnimals: []
});
export default () => ({
type: RESET_ANIMAL_SENSES,
payload: JSON.parse(data)
});
When we are using stringify the connectivity has been ended and the new state has been added but i don't know why this is not working without JSON.stringify()?
Reducer
import { SELECT_VISION } from '../actions/select_vision_type';
import { CHANGE_ANIMAL_VIDEO_STATE } from '../actions/change_animal_video_state';
import { UPDATE_ANIMALS } from '../actions/update_animals';
import { RESET_ANIMAL_SENSES } from '../actions/reset_animal_senses';
export default (state = {}, action) => {
let newState = state;
switch (action.type) {
case SELECT_VISION:
newState = { ...state, ...action.payload };
break;
case CHANGE_ANIMAL_VIDEO_STATE:
newState = { ...state, ...action.payload };
break;
case UPDATE_ANIMALS:
newState = { ...state, ...action.payload };
break;
case RESET_ANIMAL_SENSES:
newState = { ...state, ...action.payload };
break;
default:
break;
}
return newState;
};
Spread Operator in payload Solved this issue
export const RESET_ANIMAL_SENSES = 'actions/reset_animal_senses';
const data = {
selectedVision: '',
selectedState: '',
selectedAnimal: '',
viewedVisions: [''],
viewedAnimals: []
};
export default () => ({
type: RESET_ANIMAL_SENSES,
payload: { ...data } // here is the solution
});
Try this out, I'd do good amount of refactors to your reducer.
import { SELECT_VISION } from '../actions/select_vision_type';
import { CHANGE_ANIMAL_VIDEO_STATE } from '../actions/change_animal_video_state';
import { UPDATE_ANIMALS } from '../actions/update_animals';
import { RESET_ANIMAL_SENSES } from '../actions/reset_animal_senses';
const initialState = {
selectedVision: '',
selectedState: '',
selectedAnimal: '',
viewedVisions: [''],
viewedAnimals: []
}
export default (state = initialState, action) => {
switch (action.type) {
// since all the cases have common code.
case SELECT_VISION:
case CHANGE_ANIMAL_VIDEO_STATE:
case UPDATE_ANIMALS: {
return { ...state, ...action.payload }
}
case RESET_ANIMAL_SENSES: {
return { ...initialState }
}
default: {
return state;
}
}
};
Try this reducer once. However, currently I don't have a clarity on why would it work with stringify in place.
Related
I have a Redux reducer which handles among other things products. Each product has an array field named productImages. An action type DELETE_PRODUCT_IMAGE_SUCCESS removes a specific image from that array.
How can I automatically delete a product once all its productImages are removed?
I've tried using useEffect to no avail.
My codesandbox is available here.
case appConstants.DELETE_PRODUCT_IF_NO_IMAGE:
return {
...state,
products: state.products.filter(
(product) => product?.productImages?.length > 0
)
};
You could update the list when you delete an image from the product.
case appConstants.DELETE_PRODUCT_IMAGE_SUCCESS:
return {
...state,
products: state?.products
.map((item, index) => {
if (index !== action.payload?.productIndex) return item;
return {
...item,
productImages: item?.productImages.filter(
({ imageFileName = null }) =>
imageFileName !== action?.payload?.imageFileName
)
};
})
.filter((product) => product?.productImages?.length > 0)
};
case appConstants.DELETE_PRODUCT_IF_NO_IMAGE:
return state;
It seems you are calling the purge method only once when the app loads:
useEffect(() => {
dispatch(deleteProductIfNoImage());
}, [dispatch]);
A more efficient way would be to introduce sub-reducers, it would make your task easier:
const product = (state, action) => {
const { productImages = [] } = state;
const { imageFileName } = action.payload || {};
switch (action.type) {
case appConstants.DELETE_PRODUCT_IMAGE_SUCCESS:
return {
...state,
productImages: productImages.filter(
(productImage) =>
productImage.imageFileName !== imageFileName
),
};
default:
return state;
}
};
const products = (state, action) => {
const { productIndex } = action.payload || {};
switch (action.type) {
case appConstants.DELETE_PRODUCT_IMAGE_SUCCESS:
return {
...state,
products: products
.map((item, index) =>
index === productIndex ? product(item) : item
)
.filter((item) => item.productImage?.length > 0),
};
default:
return state;
}
};
const appReducer = (state, action) => {
switch (action.type) {
case appConstants.DELETE_PRODUCT_IMAGE_SUCCESS:
return {
...state,
products: products(state, action),
};
default:
return state;
}
};
If you follow this sub-reducers advice which Dan Abramov suggested in his online redux course + switch to dictionaries and product ids, the reducer code would be much cleaner and possibly more maintainable:
const product = (state, action) => {
switch (action.type) {
case appConstants.CHANGE_PRODUCT_CODE:
return {
...state,
newProductCode: action.payload.productCode,
};
case appConstants.CHANGE_PRODUCT_NAME:
return {
...state,
productName: action.payload.productCode,
};
case appConstants.CHANGE_PRODUCT_CATEGORY:
return {
...state,
productName: action.payload.productCategory,
};
}
};
const products = (state = initialState, action) => {
switch (action.type) {
case appConstants.CHANGE_PRODUCT_CODE:
case appConstants.CHANGE_PRODUCT_NAME:
case appConstants.CHANGE_PRODUCT_CATEGORY:
return {
...state,
products: {
...state,
[action.id]: product(products[action.id], action)
}
}
}
};
Furthermore, I recommend checking out redux toolkit which is the new redux standard for building stores and perhaps utilizing immerJs instead of sub-reducers in your redux reducer code.
I am using React with Redux. The Redux devtool console shows that data exists in the state (redux devtools console), but the webpage displays an error saying that the object is undefined (error).
This is my code for my screen:
import React, { useEffect } from "react";
import { useSelector, useDispatch } from "react-redux";
import { listProductDetails } from "../redux/actions/productActions";
const ProductScreen = ({ match }) => {
const dispatch = useDispatch();
const productDetails = useSelector((state) => state.productDetails);
const { loading, error, product } = productDetails;
useEffect(() => {
dispatch(listProductDetails(match.params.id));
}, [dispatch, match]);
return <div>{product.name}</div>;
};
export default ProductScreen;
This is the code for my redux reducer:
import {
PRODUCT_DETAILS_FAIL,
PRODUCT_DETAILS_REQUEST,
PRODUCT_DETAILS_SUCCESS,
} from "../constants";
export const productDetailsReducer = (state = { product: {} }, action) => {
switch (action.type) {
case PRODUCT_DETAILS_REQUEST:
return { loading: true };
case PRODUCT_DETAILS_SUCCESS:
return { loading: false, product: action.payload };
case PRODUCT_DETAILS_FAIL:
return { loading: false, error: action.payload };
default:
return state;
}
};
This is the code for my action:
import axios from "axios";
import {
PRODUCT_DETAILS_FAIL,
PRODUCT_DETAILS_REQUEST,
PRODUCT_DETAILS_SUCCESS,
} from "../constants";
export const listProductDetails = (id) => async (dispatch) => {
try {
dispatch({
type: PRODUCT_DETAILS_REQUEST,
});
const { data } = await axios.get(`/api/products/${id}`);
dispatch({
type: PRODUCT_DETAILS_SUCCESS,
payload: data,
});
} catch (error) {
dispatch({
type: PRODUCT_DETAILS_FAIL,
payload:
error.response && error.response.data.message
? error.response.data.message
: error.message,
});
}
};
I really cannot find the issue here, any help would be greatly appreciated!
I think the problem is when you dispatch PRODUCT_DETAILS_REQUEST action, reducer will override the state value with { loading: true }, and so product will be undefined instead of empty object {}.
So you should return merged object with the previous state in the reducer. e.g. return { ...state, loading: true };
Hope it could help you.
export const productDetailsReducer = (state = { product: {} }, action) => {
switch (action.type) {
case PRODUCT_DETAILS_REQUEST:
return { ...state, loading: true };
case PRODUCT_DETAILS_SUCCESS:
return { ...state, loading: false, product: action.payload };
case PRODUCT_DETAILS_FAIL:
return { ...state, loading: false, error: action.payload };
default:
return state;
}
};
I don´t think this issue is bound to a specific framework or library, but applies to all store based application following the action - reducer pattern.
For clarity, I am using Angular and #ngrx.
In the application I am working on we need to track the loading state of individual resources.
The way we handle other async requests is by this, hopefully familiar, pattern:
Actions
GET_RESOURCE
GET_RESOURCE_SUCCESS
GET_RESOURCE_FAILURE
Reducer
switch(action.type)
case GET_RESOURCE:
return {
...state,
isLoading = true
};
case GET_RESOURCE_SUCCESS:
case GET_RESOURCE_FAILURE:
return {
...state,
isLoading = false
};
...
This works well for async calls where we want to indicate the loading state globally in our application.
In our application we fetch some data, say BOOKS, that contains a list of references to other resources, say CHAPTERS.
If the user wants to view a CHAPTER he/she clicks the CHAPTER reference that trigger an async call. To indicate to the user that this specific CHAPTER is loading, we need something more than just a global isLoading flag in our state.
The way we have solved this is by creating a wrapping object like this:
interface AsyncObject<T> {
id: string;
status: AsyncStatus;
payload: T;
}
where AsyncStatus is an enum like this:
enum AsyncStatus {
InFlight,
Success,
Error
}
In our state we store the CHAPTERS like so:
{
chapters: {[id: string]: AsyncObject<Chapter> }
}
However, I feel like this 'clutter' the state in a way and wonder if someone has a better solution / different approach to this problem.
Questions
Are there any best practices for how to handle this scenario?
Is there a better way of handling this?
I have faced several times this kind of situation but the solution differs according to the use case.
One of the solution would be to have nested reducers. It is not an antipattern but not advised because it is hard to maintain but it depends on the usecase.
The other one would be the one I detail below.
Based on what you described, your fetched data should look like this:
[
{
id: 1,
title: 'Robinson Crusoe',
author: 'Daniel Defoe',
references: ['chp1_robincrusoe', 'chp2_robincrusoe'],
},
{
id: 2,
title: 'Gullivers Travels',
author: 'Jonathan Swift',
references: ['chp1_gulliverstravels', 'chp2_gulliverstravels', 'chp3_gulliverstravels'],
},
]
So according to your data, your reducers should look like this:
{
books: {
isFetching: false,
isInvalidated: false,
selectedBook: null,
data: {
1: { id: 1, title: 'Robinson Crusoe', author: 'Daniel Defoe' },
2: { id: 2, title: 'Gullivers Travels', author: 'Jonathan Swift' },
}
},
chapters: {
isFetching: false,
isInvalidated: true,
selectedChapter: null,
data: {
'chp1_robincrusoe': { isFetching: false, isInvalidated: true, id: 'chp1_robincrusoe', bookId: 1, data: null },
'chp2_robincrusoe': { isFetching: false, isInvalidated: true, id: 'chp2_robincrusoe', bookId: 1, data: null },
'chp1_gulliverstravels': { isFetching: false, isInvalidated: true, id: 'chp1_gulliverstravels', bookId: 2, data: null },
'chp2_gulliverstravels': { isFetching: false, isInvalidated: true, id: 'chp2_gulliverstravels', bookId: 2, data: null },
'chp3_gulliverstravels': { isFetching: false, isInvalidated: true, id: 'chp3_gulliverstravels', bookId: 2, data: null },
},
}
}
With this structure you won't need isFetching and isInvalidated in your chapter reducers as every chapter is a separated logic.
Note: I could give you a bonus details later on on how we can leverage the isFetching and isInvalidated in a different way.
Below the detailed code:
Components
BookList
import React from 'react';
import map from 'lodash/map';
class BookList extends React.Component {
componentDidMount() {
if (this.props.isInvalidated && !this.props.isFetching) {
this.props.actions.readBooks();
}
}
render() {
const {
isFetching,
isInvalidated,
data,
} = this.props;
if (isFetching || (isInvalidated && !isFetching)) return <Loading />;
return <div>{map(data, entry => <Book id={entry.id} />)}</div>;
}
}
Book
import React from 'react';
import filter from 'lodash/filter';
import { createSelector } from 'reselect';
import map from 'lodash/map';
import find from 'lodash/find';
class Book extends React.Component {
render() {
const {
dispatch,
book,
chapters,
} = this.props;
return (
<div>
<h3>{book.title} by {book.author}</h3>
<ChapterList bookId={book.id} />
</div>
);
}
}
const foundBook = createSelector(
state => state.books,
(books, { id }) => find(books, { id }),
);
const mapStateToProps = (reducers, props) => {
return {
book: foundBook(reducers, props),
};
};
export default connect(mapStateToProps)(Book);
ChapterList
import React from 'react';
import { connect } from 'react-redux';
import { createSelector } from 'reselect';
import map from 'lodash/map';
import find from 'lodash/find';
class ChapterList extends React.Component {
render() {
const { dispatch, chapters } = this.props;
return (
<div>
{map(chapters, entry => (
<Chapter
id={entry.id}
onClick={() => dispatch(actions.readChapter(entry.id))} />
))}
</div>
);
}
}
const bookChapters = createSelector(
state => state.chapters,
(chapters, bookId) => find(chapters, { bookId }),
);
const mapStateToProps = (reducers, props) => {
return {
chapters: bookChapters(reducers, props),
};
};
export default connect(mapStateToProps)(ChapterList);
Chapter
import React from 'react';
import { connect } from 'react-redux';
import { createSelector } from 'reselect';
import map from 'lodash/map';
import find from 'lodash/find';
class Chapter extends React.Component {
render() {
const { chapter, onClick } = this.props;
if (chapter.isFetching || (chapter.isInvalidated && !chapter.isFetching)) return <div>{chapter.id}</div>;
return (
<div>
<h4>{chapter.id}<h4>
<div>{chapter.data.details}</div>
</div>
);
}
}
const foundChapter = createSelector(
state => state.chapters,
(chapters, { id }) => find(chapters, { id }),
);
const mapStateToProps = (reducers, props) => {
return {
chapter: foundChapter(reducers, props),
};
};
export default connect(mapStateToProps)(Chapter);
Book Actions
export function readBooks() {
return (dispatch, getState, api) => {
dispatch({ type: 'readBooks' });
return fetch({}) // Your fetch here
.then(result => dispatch(setBooks(result)))
.catch(error => dispatch(addBookError(error)));
};
}
export function setBooks(data) {
return {
type: 'setBooks',
data,
};
}
export function addBookError(error) {
return {
type: 'addBookError',
error,
};
}
Chapter Actions
export function readChapter(id) {
return (dispatch, getState, api) => {
dispatch({ type: 'readChapter' });
return fetch({}) // Your fetch here - place the chapter id
.then(result => dispatch(setChapter(result)))
.catch(error => dispatch(addChapterError(error)));
};
}
export function setChapter(data) {
return {
type: 'setChapter',
data,
};
}
export function addChapterError(error) {
return {
type: 'addChapterError',
error,
};
}
Book Reducers
import reduce from 'lodash/reduce';
import { combineReducers } from 'redux';
export default combineReducers({
isInvalidated,
isFetching,
items,
errors,
});
function isInvalidated(state = true, action) {
switch (action.type) {
case 'invalidateBooks':
return true;
case 'setBooks':
return false;
default:
return state;
}
}
function isFetching(state = false, action) {
switch (action.type) {
case 'readBooks':
return true;
case 'setBooks':
return false;
default:
return state;
}
}
function items(state = {}, action) {
switch (action.type) {
case 'readBook': {
if (action.id && !state[action.id]) {
return {
...state,
[action.id]: book(undefined, action),
};
}
return state;
}
case 'setBooks':
return {
...state,
...reduce(action.data, (result, value, key) => ({
...result,
[key]: books(value, action),
}), {});
},
default:
return state;
}
}
function book(state = {
isFetching: false,
isInvalidated: true,
id: null,
errors: [],
}, action) {
switch (action.type) {
case 'readBooks':
return { ...state, isFetching: true };
case 'setBooks':
return {
...state,
isInvalidated: false,
isFetching: false,
errors: [],
};
default:
return state;
}
}
function errors(state = [], action) {
switch (action.type) {
case 'addBooksError':
return [
...state,
action.error,
];
case 'setBooks':
case 'setBooks':
return state.length > 0 ? [] : state;
default:
return state;
}
}
Chapter Reducers
Pay extra attention on setBooks which will init the chapters in your reducers.
import reduce from 'lodash/reduce';
import { combineReducers } from 'redux';
const defaultState = {
isFetching: false,
isInvalidated: true,
id: null,
errors: [],
};
export default combineReducers({
isInvalidated,
isFetching,
items,
errors,
});
function isInvalidated(state = true, action) {
switch (action.type) {
case 'invalidateChapters':
return true;
case 'setChapters':
return false;
default:
return state;
}
}
function isFetching(state = false, action) {
switch (action.type) {
case 'readChapters':
return true;
case 'setChapters':
return false;
default:
return state;
}
}
function items(state = {}, action) {
switch (action.type) {
case 'setBooks':
return {
...state,
...reduce(action.data, (result, value, key) => ({
...result,
...reduce(value.references, (res, chapterKey) => ({
...res,
[chapterKey]: chapter({ ...defaultState, id: chapterKey, bookId: value.id }, action),
}), {}),
}), {});
};
case 'readChapter': {
if (action.id && !state[action.id]) {
return {
...state,
[action.id]: book(undefined, action),
};
}
return state;
}
case 'setChapters':
return {
...state,
...reduce(action.data, (result, value, key) => ({
...result,
[key]: chapter(value, action),
}), {});
},
default:
return state;
}
}
function chapter(state = { ...defaultState }, action) {
switch (action.type) {
case 'readChapters':
return { ...state, isFetching: true };
case 'setChapters':
return {
...state,
isInvalidated: false,
isFetching: false,
errors: [],
};
default:
return state;
}
}
function errors(state = [], action) {
switch (action.type) {
case 'addChaptersError':
return [
...state,
action.error,
];
case 'setChapters':
case 'setChapters':
return state.length > 0 ? [] : state;
default:
return state;
}
}
Hope it helps.
I'm trying to pass some value from a component to a action creators which is doing a get request with axios. I'm trying to follow this pattern from Dan Abramov :
export const SOME_ACTION = 'SOME_ACTION';
export function someAction() {
return (dispatch, getState) => {
const {items} = getState().otherReducer;
dispatch(anotherAction(items));
}
}
However I can't make it work. I think I have trouble on two level : my component and my action creator. Would be great to have some helps.
my component :
const timeR = ({
selectedTimeRange,
timeRange = [],
onTimeChange }) => {
return (
<div>
<div>
Filters:
<div>
Year:
<select
defaultValue={selectedTimeRange}
onChange={onTimeChange}>
<option value="all" >All</option>
{timeRange.map((y, i) =>
<option key={i} value={y}>{y}</option>
)}
</select>
</div>
</div>
</div>
);
}
function mapStateToProps(state) {
var range = ['30daysAgo', '15daysAgo', '7daysAgo'];
return {
selectedTimeRange: state.timeReducer.timerange[0],
timeRange: range
};
};
const mapDispachToProps = (dispatch) => {
return {
onTimeChange: (e) => {dispatch (onSetTimeRange(e.target.value));},
};
};
const TimeRange = connect(mapStateToProps, mapDispachToProps)(timeR);
export default TimeRange;
This component give me a dropdown menu. When selecting a timerange, for example '30daysAgo', it update my redux store state so I can access the value from my reducer.
Here is the action associated to my dropdown menu :
export function onSetTimeRange(timerange) {
return {
type: 'SET_TIME_RANGE',
timerange
}
}
and here is the action dealing with axios.get :
export const fetchgadata = () => (dispatch) => {
dispatch({
type: 'FETCH_DATA_REQUEST',
isFetching:true,
error:null
});
var VIEW_ID = "ga:80820965";
return axios.get("http://localhost:3000/gadata", {
params: {
id: VIEW_ID
}
}).then(response => {
dispatch({
type: 'FETCH_DATA_SUCCESS',
isFetching: false,
data: response.data.rows.map( ([x, y]) => ({ x, y }) )
});
})
.catch(err => {
dispatch({
type: 'FETCH_DATA_FAILURE',
isFetching:false,
error:err
});
console.error("Failure: ", err);
});
};
My question :
How do I bring these two actions together. At the end I would like to be able, when doing onChange on my drop-down menu, to call a action with the value selected from my menu as a param for my axios.get request.
I feel like I need to nest two actions creators. I've tried this but doesn't work ("fetchgadata" is read-only error in my terminal)
export const SET_TIME_RANGE = 'SET_TIME_RANGE';
export function onSetTimeRange() {
return (dispatch, getState) => {
const {VIEW_ID} = getState().timerange;
dispatch(fetchgadata = (VIEW_ID) => (dispatch) => {
dispatch({
type: 'FETCH_DATA_REQUEST',
isFetching:true,
error:null,
id:VIEW_ID,
});
});
return axios.get("http://localhost:3000/gadata", {
params: {
id: VIEW_ID
}
}).then(response => {
dispatch({
type: 'FETCH_DATA_SUCCESS',
isFetching: false,
data: response.data.rows.map( ([x, y]) => ({ x, y }) )
});
})
.catch(err => {
dispatch({
ype: 'FETCH_DATA_FAILURE',
isFetching:false,
error:err
});
console.error("Failure: ", err);
});
}
}
Edit:
reducers for API call :
const initialState = {data:null,isFetching: false,error:null};
export const gaData = (state = initialState, action)=>{
switch (action.type) {
case 'FETCH_DATA_REQUEST':
case 'FETCH_DATA_FAILURE':
return { ...state, isFetching: action.isFetching, error: action.error };
case 'FETCH_DATA_SUCCESS':
return Object.assign({}, state, {data: action.data, isFetching: action.isFetching,
error: null });
default:return state;
}
};
reducers for Drop-down :
const items = [{timerange: '30daysAgo'},{timerange: '15daysAgo'},{timerange: '7daysAgo'}]
const timeReducer = (state = {
timerange: items
}, action) => {
switch (action.type) {
case 'SET_TIME_RANGE':
console.log(state,action);
return {
...state,
timerange: action.timerange,
};
default:
return state;
}
}
I see a little typo in the catch of your axios.get request, it reads ype: FETCH_DATA_FAILURE. Otherwise, can you add in your reducer for me, I don't see it up there? If I understand correctly, you want one action to update two different pieces of state, in which case you would simply dispatch an action and add it to both reducers. Really it's best to just demonstrate:
//axios call
axios.get("some route", { some params } )
.then(response => {
dispatch({
type: UPDATE_TWO_THINGS,
payload: some_value
})
}) .... catch, etc
//reducer 1
import { UPDATE_TWO_THINGS } from 'types';
const INITIAL_STATE = { userInfo: '' };
export default function (state = INITIAL_STATE, action) {
switch(action.type) {
case UPDATE_TWO_THINGS:
return {...state, userInfo: payload };
}
return state;
}
//reducer 2
import { UPDATE_TWO_THINGS } from 'types';
const INITIAL_STATE = { businessInfo: '' };
export default function (state = INITIAL_STATE, action) {
switch(action.type) {
case UPDATE_TWO_THINGS:
return {...state, businessInfo: payload };
}
return state;
}
Hopefully this helps, but let me know if not, I'll do my best to get this working with you! Thanks for asking!
How to get reducers not to return always new state? Is my solution ok or there are some better way?
My state shape:
userList: {
id: 'xxx', // <-|- Not mutable by reducers fields, so using combineReducers for each field is frustrating.
ba: 'xxx', // <-|
fo: 'xxx', // <-|
users: [
{
id: 'yyy',
be: 'yyy',
fo: 'yyy',
photo: {
id: 'zzz',
url: 'http://image.jpg', <-- The only field, that changes by reducers.
},
},
...
],
}
My current reducers:
// Always returns new object.
const userListReducer = (userList, action) => {
return {
...userList,
users: usersReducer(userList, action),
}
};
// Always returns new array.
const usersReducer = (users, action) => {
return users.map(user => userReducer(user, action));
};
// Always returns new object too.
const userReducer = (user, action) => {
return {
...user,
photo: photoReducer(user.photo, action),
};
};
// The only one true reducer.
const photoReducer = (photo, action) => {
switch (action.type) {
case 'update_photo':
return {
...photo,
url: action.url,
};
default:
return photo;
}
};
Solutions
1). Call usersReducer when it's necessary. Bad part: we need to care about logic other reducers.
const userListReducer = (userList, action) => {
switch (action.type) {
case 'update_photo':
return {
...userList,
users: usersReducer(userList, action),
};
default:
return userList;
}
};
2). Using combineReducers. Bad part: we need to care about all usersList's shape. Also, this still doesn't work, because usersReducer always returns new array.
const userListRecuer = combineReducers({
id: id => id,
ba: ba => ba,
fo: fo => fo,
users: usersReducer,
});
3). My solution. Using mergeOrReturnOld and mapOrReturnOld helpers.
const userListReducer = (userList, action) => {
return mergeOrReturnOld(userList, {
users: usersReducer(userList, action),
});
};
const usersReducer = (users, action) => {
return mapOrReturnOld(users, user => userReducer(user, action));
};
const userReducer = (user, action) => {
return mergeOrReturnOld(user, {
photo: photoReducer(user.photo, action),
});
};
helpers implementation:
const mergeOrReturnOld = (obj, addition) => {
let hasChanged = false;
for (let key in addition) {
if (addition.hasOwnProperty(key)) {
if (obj[key] !== addition[key]) {
hasChanged = true;
}
}
}
if (!hasChanged) {
return obj;
} else {
return {
...obj,
...addition,
};
}
};
const mapOrReturnOld = (array, callback) => {
let hasChanged = false;
const newArray = array.map(item => {
const newItem = callback(item);
if (newItem !== item) {
hasChanged = true;
}
return newItem;
});
if (!hasChanged) {
return array;
} else {
return newArray;
}
};